code: def test_x_equals_y():
      """Test that a runtime warning is raised when no maxima are found"""
      x = range(10)
      y = [1] * len(x)
      with pytest.warns(RuntimeWarning):
          KneeLocator(x, y)
  
file_path: yellowbrick/tests/test_utils/test_kneed.py
imports: import pytest
  import matplotlib.pyplot
  import numpy
  from yellowbrick.utils.kneed import KneeLocator
label_desc: Use image node_id 9 for calling a global function with example usage: test_x_equals_y() without return types